Many tomato-based products such as tomato ketchups, barbecue sauces, pizza sauces and other similar condiments are made using slurries of tomato pastes, tomato purees, tomato juices or similar compositions that contain substantial amounts of tomato solids. As used herein, sources of tomato solids generally comprise, but are not limited to, concentrates of one or a combination of the liquid obtained from mature tomato fruit (such as the fruit of Lycopersilum esculentum P. Mill); the liquid obtained from the residue from preparing tomatoes for canning; and the liquid obtained from the residue from the partial extraction of juice from tomatoes.
Tomato pastes, as used herein, refers to concentrates having a net total tomato solids content of at least about 24% by weight or more, or such other solids content generally recognized in the art as sufficient for a tomato paste. Tomato pastes intended for further processing into other food products generally contain about 30% to about 32% net total tomato solids. As referred to herein, a product's net total tomato solids content is typically determined by evaporative methods known to the art, such as microwave moisture analysis or evaporative oven analysis techniques.
Tomato puree, as used herein, refers to concentrates or products (if not concentrated) containing between about 8% to about 24% by weight tomato solids or such other solids content recognized as sufficient for tomato puree. Tomato juice, as used herein, refers to a concentrate or product (if not concentrated) having between about 5% to about 8% by weight tomato solids, or such other solids content recognized as sufficient for tomato juice. Such pastes, purees, sauces and juices may also contain salts, spices, sugars, thickeners, coloring and other such additives. Unless otherwise specifically identified, the above mentioned tomato products may be collectively referred to herein as "tomato sauces" or "tomato slurries".
The tomato solids in such tomato sauces or slurries typically include tomato pulp, comprising primarily water-insoluble tomato particles, tomato seeds and portions of tomato skins; tomato fibers which comprise the bulk of the tomato fruit; and pectin, a naturally occurring polysaccharide found in the tomato fruit. Each of these components affect the appearance, flavor and sensory appeal of tomato-based food products.
For example, the carotene pigment that gives tomato sauce its characteristic red color is found primarily in chromoplasts within the tomato pulp and tomato fiber. Hence, the amount and distribution of the pulp and fiber will determine whether the tomato sauce will have an overall, even desirable color. In addition, the size and distribution of the tomato pulp particles may also affect the texture of such tomato- based products. Large, unevenly distributed pulp particles will tend to produce a lumpy product, while extremely finely divided pulp particles will tend to produce a smooth textured product.
Similarly, the tomato fibers tend to link together and intertwine to form a lattice network or fibrous matrix that provides body and viscosity to tomato-based products and further traps free liquid which would otherwise "weep", i.e. separate, from the product. The liquid typically consists primarily of water and may also include other tomato fluids, and additives to the product. When present in sufficient concentrations, the pectin in tomato-based products forms a gel that also acts to bind free liquid in the products and to increase the products' viscosity.
In addition, tomato pastes, as well as other tomato-based products, may be identified by their "screen size". This is an indication of the average maximum size of particulate matter in the product such as tomato fibers, skin sections, and seeds. For example, a 0.060 screen tomato paste refers to a paste that was passed through a screen with 0.060 inch diameter openings, and a 0.045 screen tomato paste refers to a paste passed through a screen with 0.045 inch diameter opening.
It is known to modify the physical properties of the tomato solids in tomato sauces and slurries using various techniques, including homogenization of the products. The treatment of tomato slurries with homogenizers was known to affect the size and distribution of tomato pulp particles, the nature of the fibrous materials in the tomato solids, and the amount of pectin released from the tomato solids. For example, when properly applied, homogenization may finely divide, break down and disperse pulp particles through out a slurry to produce products with acceptable colors and textures.
It further was recognized that homogenization of the products affects the matrix or lattice network created by the interlinking of tomato fibers. As with other types of processing, homogenization tends to reduce the length of individual tomato fibers and to fray or fibrillate the ends of those fibers. Under the proper conditions, homogenization will sufficiently fibrillate the tomato fibers to permit the frayed ends of those fibers to absorb and hold greater amounts of liquid in the product and to prevent weeping of liquid from the product.
It also was recognized that homogenization of a tomato slurry may release additional pectin from the tomato pulp and fibers and more evenly distribute that gel-forming compound throughout the product. This typically increased the viscosity of the product and the amount of serum retained by the product. Thus, it was recognized that when homogenized under the proper conditions, tomato sauces could attain viscosities equal to that of unhomogenized products containing 10-15% more net total tomato solids.
However, it was recognized that the homogenization conditions must be carefully balanced to avoid undesirable side effects. Such side effects include overprocessing the tomato sauce or slurry so that it loses its desirable texture and becomes too smooth. Overprocessing with a homogenizer further reduces the length of the fibrous materials within a tomato-based product to the point where those fibers cannot effectively form a lattice network in the product. This may result in an unacceptable color, texture and appearance, and a failure of the product to trap and hold significant amounts of tomato liquid.
Hence, the homogenization conditions, particularly homogenization pressures, were carefully controlled to balance the advantages of increased uniformity and increased viscosity with the potential for overprocessing and damage to the viscosity enhancing elements of the tomato solids. When preparing tomato-based products, the generally recommended maximum homogenization pressures were typically from about 2,500 psi (172 bar) to about 3,000 psi (207 bar), and it was believed that homogenization at pressures greater than about 3,000 psi (207 bar) should be avoided. (All references to pressure herein are to gauge). Homogenization at higher pressures was believed to provide some increase in the viscosity of the tomato-based products, but also produced unacceptable degradation of other important product properties, such as those mentioned above. Other alternative processing steps were used to supplement the effects of homogenization, including the additional steps of milling the products or using of vacuum expansion chambers to increase viscosity and improve the color of the products. In addition, food grade acetic acids and citric acids were sometimes used as pretreatment additives to improve the viscosity of such tomato sauces.
As discussed below, the present invention provides a method for high pressure, high shear homogenization of tomato sauces at pressures well in excess of the previously recommended maximum of about 3,000 psi (207 bar). The invention provides tomato-based products with viscosities in excess of products with similar tomato solids content homogenized at lower pressures, and without the deleterious effects described by others in the art. Furthermore, the invention is capable of providing a product with a reduced tomato solids content but with a viscosity, and other physical characteristics comparable to products with a significantly higher tomato solids content.